Variable valve apparatus for internal combustion engine

ABSTRACT

In order to simultaneously exert a plurality of functions such as execution of internal EGR, application of engine braking, improvement in fuel consumption and purification of exhaust gas, a variable valve apparatus for an internal combustion engine of the invention includes a cam shaft arranged to be rotatable on a cylinder head of the internal combustion engine, a rocker shaft arranged to be capable of oscillation in the internal combustion engine, a continuous variable rocker arm mechanism which is driven by a cam formed on the cam shaft, opens or closes air intake valves and exhaust valves, and continuously makes a lift of the valves variable, and a switching rocker arm mechanism which is driven by the cam formed on the cam shaft, opens or closes the air intake valves and the exhaust valves, and switches the lift of the valves in a stepwise manner.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation application of PCT Application No.PCT/JP2008/073635, filed Dec. 25, 2008, which was published under PCTArticle 21(2) in Japanese.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2007-338360, filed Dec. 27, 2007;and No. 2008-004745, filed Jan. 11, 2008, the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable valve apparatus for aninternal combustion engine which makes it possible to change drivephases and valve lifts of an air intake valve, an exhaust valve, and thelike. 2. Description of the Related Art

In an internal combustion engine such as an automobile engine, avariable valve apparatus is known which changes drive phases and liftsof intake/exhaust valves depending on driving states of the internalcombustion engine to purify an exhaust gas discharged from the engine orto reduce a fuel consumption of the automobile.

As the variable valve apparatus, a variable valve apparatus having acontinuous variable rocker arm mechanism is known in which a third armis arranged between a first arm which drives a valve and a second armcaused to oscillate by a cam, the valve is driven through the third arm,and a fulcrum of oscillation of the second arm is displaced tocontinuously change the phase and lift of the valve (for example, seeJpn. Pat. Appln. KOKAI Publication No. 2004-339079).

The variable valve apparatus having the continuous variable rocker armmechanism adjusts the lift and phase of a valve to purify an exhaust gasand adjusts an opening valve angle to make it possible to improve a fuelconsumption.

On the other hand, a variable valve apparatus having a switching rockerarm mechanism is known in which a mechanism which selectively transmitsdisplacement is arranged between the first arm which drives the valveand the second arm caused to oscillate by the cam to operate or stop thefirst arm (for example, see Jpn. Pat. Appin. KOKAI Publication No.2005-105953).

The variable valve apparatus having the switching rocker arm mechanismperforms internal EGR by opening an exhaust valve in an intake stroke tomake it possible to purify an exhaust gas and opens the exhaust valve ata compression top dead center to make it possible to apply the enginebraking.

BRIEF SUMMARY OF THE INVENTION

However, the variable valve apparatus as described above must select anyone of a switching rocker arm mechanism 40 and a continuous variablerocker arm mechanism 50, and can exert only one of the functions of themechanisms. Furthermore, although the switching rocker arm mechanism 40can be instantaneously operated, the switching rocker arm mechanism 40cannot be finely adjusted in lift and phase of the valve. On the otherhand, although the continuous variable rocker arm mechanism 50 can befinely adjusted in lift and phase, the continuous variable rocker armmechanism 50 requires about one second for an operation and has poorresponsiveness.

Therefore, it is an object of the present invention to provide avariable valve apparatus for an internal combustion engine which canexecute internal EGR and apply engine braking and can simultaneouslyexert a plurality of functions such as improvement in fuel consumptionand purification of an exhaust gas.

In order to solve the problem and achieve the object, the variable valveapparatus for an internal combustion engine of the present invention hasthe following configuration.

A variable valve apparatus for an internal combustion engine, comprisesa cam shaft arranged to be rotatable on a cylinder head of the internalcombustion engine; a rocker shaft arranged to be capable of oscillationin the internal combustion engine; a continuous variable rocker armmechanism which is driven by a cam formed on the cam shaft, opens orcloses at least one of an air intake valve and an exhaust valve, andcontinuously makes a lift of the valve variable; and a switching rockerarm mechanism which is driven by the cam formed on the cam shaft, opensor closes at least one of the air intake valve and the exhaust valve,and switches the lift of the valve in a stepwise manner.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view showing a main part of a cylinder block in which avariable valve apparatus according to the present invention isincorporated.

FIG. 2 is a sectional view showing the cylinder head block cut alongline A-A in FIG. 1 when viewed in a direction given by an arrow.

FIG. 3 is a sectional view showing the cylinder head block cut alongline B-B in FIG. 1 when viewed in a direction given by an arrow.

FIG. 4 is a perspective view showing the variable valve apparatus.

FIG. 5 is an exploded perspective view showing the variable valveapparatus.

FIG. 6 is an explanatory diagram showing a control concept in executionof internal EGR.

FIG. 7 is an explanatory diagram showing a control concept in executionof internal EGR.

FIG. 8 is a sectional view showing an operation of a switching rockerarm mechanism in a normal operation.

FIG. 9 is a sectional view showing an operation of a continuous variablerocker arm mechanism in a normal operation.

FIG. 10 is a sectional view showing an operation of the switching rockerarm mechanism in execution of internal EGR.

FIG. 11 is a sectional view showing an operation of the continuousvariable rocker arm mechanism in execution of internal EGR.

FIG. 12 is an explanatory diagram showing a control concept inapplication of engine braking.

FIG. 13 is an explanatory diagram showing a control concept inapplication of engine braking.

FIG. 14 is a sectional view showing an operation of the switching rockerarm mechanism in application of engine braking.

FIG. 15 is a sectional view showing an operation of the continuousvariable rocker arm mechanism in application of engine braking.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a plan view showing a main part of a cylinder head 10 in whicha variable valve apparatus 20 for an internal combustion engineaccording to a first embodiment of the invention is incorporated, FIG. 2is a sectional view showing the cylinder head 10 cut along line A-A inFIG. 1 when viewed in a direction given by an arrow, FIG. 3 is asectional view showing the cylinder head 10 cut along line B-B in FIG. 1when viewed in a direction given by an arrow, FIG. 4 is a perspectiveview showing the variable valve apparatus 20, and FIG. 5 is an explodedperspective view showing the variable valve apparatus 20.

As shown in FIGS. 1 to 3, one pair of air intake valves 12 and 13 andone pair of exhaust valves 14 and 15 are arranged on the cylinder head10. The air intake valves 12 and 13 are arranged in an intake path 10 aof the cylinder head 10 such that the air intake valves 12 and 13 can bereciprocated in an axial direction, and the air intake valves 12 and 13are always biased in such a direction that the intake path 10 a isclosed by valve springs 12 a and 13 a. The exhaust valves 14 and 15 arearranged in an exhaust path 10 b of the cylinder head 10 such that theexhaust valves 14 and 15 can be reciprocated in the axial direction, andthe exhaust valves 14 and 15 are always biased in such a direction theintake path 10 a is closed by valve springs 14 a and 15 a. The cylinder11 is attached to a cylinder block (not shown) located below thecylinder head 10.

The variable valve apparatus 20 is a valve operation apparatus whichopens/closes valves of an internal combustion engine. One pair ofvariable valve apparatuses 20 is arranged to sandwich the cylinder 11.Since the one pair of variable valve apparatuses 20 has a structuresymmetrical with reference to the cylinder 11, only the variable valveapparatus 20 on the exhaust valves 14 and 15 side will be explained, andan explanation of the variable valve apparatus 20 on the air intakevalves 12 and 13 side is not explained.

The cylinder head 10 comprises one pair of cam shafts 21 arranged to berotatable, one pair of rocker shafts 30 arranged to be capable ofoscillation, one pair of switching rocker arm mechanisms 40 which aredriven by a cam 22 formed on the cam shaft 21 and open and close the airintake valves 12 and 13 and the exhaust valves 14 and 15 and switchlifts of the air intake valves 12 and 13 and the exhaust valves 14 and15 in a stepwise manner, and one pair of continuous variable rocker armmechanisms 50 which are driven by a cam 23 formed on the cam shaft 21and open and close the air intake valves 12 and 13 and the exhaustvalves 14 and 15 and continuously make the lifts variable. The switchingrocker arm mechanisms 40 and the continuous variable rocker armmechanisms 50 share a rocker arm 60.

The cam shafts 21 and the rocker shafts 30 are connected to a crankshaft (not shown) of an internal combustion engine through a cam chain,gears, and the like. When the crank shaft is rotated, the cams 22 and 23having different cam profiles are rotationally driven in a directionindicated by an arrow R. The cams 22 and 23 drive the variable valveapparatus 20 at a predetermined timing described later.

An oil path 31 to which engine oil is supplied is arranged inside therocker shaft 30. An oil pressure supply mechanism 80 which supplies theengine oil to the oil path 31 is connected to the oil path 31. Therocker shaft 30 comprises a drive mechanism 90 which controls arotational angle position about a shaft center line of the rocker shaft30. Furthermore, a notch 32 is formed in the rocker shaft 30 at aposition corresponding to the continuous variable rocker arm mechanism50.

With reference to FIGS. 2 and 5, the switching rocker arm mechanism 40will be explained. The switching rocker arm mechanism 40 comprises theshared rocker arm 60 supported by the rocker shafts 30 to be capable ofoscillation and formed to make it possible to drive the exhaust valves14 and 15, and a switching rocker arm 41 driven by the cam 22 andarranged to be capable of oscillation on the rocker shaft 30.

In the switching rocker arm 41, a boss portion 41 a supported by therocker shaft 30 to be capable of oscillation is formed; a strike arm 41b which projects upwardly from the boss portion 41 a, enters a windowportion 71 b of a vertical piston structure 70 serving as a transmissionmechanism described later, and retreats from the window portion 71 b isformed; and a roller 41 c capable of oscillation is formed. When theroller 41 c is brought into contact with the cam 22 to rotate the cam22, the switching rocker arm 41 is caused to oscillate by using a shaftcenter line of the rocker shaft 30 as a fulcrum. A trench 41 d is formedin the switching rocker arm 41.

Reference number 42 in FIG. 5 denotes a torsion coil spring. A bentportion 42 a is formed on one end side of the spring, and a movingportion 42 b extending in an axial direction of the rocker shafts 30 andbent to the outside in the radial direction is formed on the other endside of the spring. The bent portion 42 a is inserted into the cylinderhead 10. When the moving portion 42 b of the torsion coil spring 42 isengaged in the trench 41 d, the torsion coil spring 42 biases theswitching rocker arm 41 such that the roller 41 c moves along the linesof the cam 22.

The shared rocker arm 60 comprises a boss portion 61 fitted in therocker shaft 30 portion to be capable of oscillation, arms 62 and 63extending from the boss portion 61 to the exhaust valves 14 and 15, anda pressed portion 64 pressed by a pressing portion 53 b described later.In the boss portion 61, a flow path 61 a which guides the engine oilfrom the oil path 31 is formed.

In the boss portion 61, as a transmission mechanism to selectivelytransmit displacement from the switching rocker arm 41 to the sharedrocker arm 60, the cylindrical vertical piston structure 70 is arranged.The vertical piston structure 70 comprises a storage tube 71 having ahollow portion 71 a continuing to an internal surface of the bossportion 61 and the window portion 71 b on the side surface, a lid member72 which blocks an upper-end opening of the hollow portion 71 a of thestorage tube 71, a piston 73 reciprocatingly stored in the hollowportion 71 a, and a spring 74 arranged on the lid member 72 to bias thepiston 73 on the boss portion 61 side. A notch 73 a is formed in thepiston 73. The notch 73 a is generally set such that the notch 73 a islocated at a position of the window portion 71 b by the operation of thespring 74. When oil pressure is applied by the oil pressure supplymechanism 80, engine oil is supplied from the oil path 31 to the hollowportion 71 a to compress the spring 74 and push up the piston 73. Inthis manner, a circumference of the piston 73 is exposed to the windowportion 71 b. In contrast to this, when the oil pressure is released,the piston 73 is pushed down by the operation of the spring 74. Anon/off operation of the oil pressure can be instantaneously performed.

The strike arm 41 b is arranged to face the window portion 71 b. Thestrike arm 41 b is formed to have a shape such that the strike arm 41 bidly moves in the notch 73 a when the notch 73 a is positioned at thewindow portion 71 b and moves while being struck on the circumferenceportion of the piston 73 when the circumference portion is positioned atthe window portion 71 b.

In this manner, in the structure, when the strike arm 41 b of theswitching rocker arm 41 is not struck on the piston 73, cam displacementfrom the switching rocker arm 41 is not transmitted to the shared rockerarm 60. When the strike arm 41 b is struck on the piston 73, the camdisplacement from the switching rocker arm 41 opens the exhaust valves14 and 15 through the shared rocker arm 60. An oil discharge chamber 32having a width larger than that of the flow path 61 a is formed in therocker shaft 30 on the downstream side of the oil path 31, so that theengine oil can be supplied to the hollow portion 71 a even when theposition of the flow path 61 a is changed by oscillation of the rockershaft 30 itself or oscillation of the switching rocker arm 41 withrotation of the cam 22. The width of the oil discharge chamber 32 ispreferably larger than a distance of oscillation of the switching rockerarm 41 and preferably set to a width at which the engine oil can besupplied to the flow path 61 a even when the rocker shaft 30 reaches theposition of maximum oscillation.

Furthermore, an oil supply chamber 75 having a width larger than that ofthe flow path 61 a is formed in the vertical piston structure 70 on anupstream side of the hollow portion 71 a. Even when the switching rockerarm 41 is caused to oscillate with rotation of the cam 22 to change theposition of the flow path 61 a, the engine oil can be supplied to thehollow portion 71 a. The width of the oil supply chamber 75 ispreferably larger than a distance of oscillation of the switching rockerarm 41.

The continuous variable rocker arm mechanism 50 will be explained withreference to FIGS. 3 and 5. The continuous variable rocker arm mechanism50 comprises the shared rocker arm 60 supported by the rocker shaft 30to be capable of oscillation and formed to make it possible to drive theexhaust valves 14 and 15, a continuous variable arm 53 driven by the cam23 and arranged to be capable of oscillation about a fulcrum Q set onthe rocker shaft 30 side, and an intermediate arm 51 which is arrangedbetween the shared rocker arm 60 and the continuous variable arm 53 andtransmits oscillation displacement of the continuous variable arm 53 tothe shared rocker arm 60 to drive the shared rocker arm 60.

The intermediate arm 51 comprises an annular shaft fitting portion 51 aand a pressing portion 51 b projecting from the shaft fitting portion 51a in a radial direction. A roller 51 c is arranged on the pressingportion 51 b. When the intermediate arm 51 is caused to oscillate aboutthe rocker shaft 30, the pressing portion 53 b presses the pressedportion 64 of the shared rocker arm 60, and the shared rocker arm 60opens the exhaust valves 14 and 15.

The continuous variable arm 53 comprises a connection member 54 whichconnects the continuous variable arm 53 and the rocker shaft 30. Theconnection member 54 is a stud bolt, has a spherical universal coupling54 a on one end side thereof, is screwed into a screw hole 33 formed inthe notch 32 of the rocker shaft 30, and is fixed by a lock nut 54 b.When the connection member 54 is fixed to the rocker shaft 30, theuniversal coupling 54 a functions as the fulcrum Q.

Reference number 55 in FIG. 5 denotes a torsion coil spring. The torsioncoil spring 55 has a bent portion 55 a formed on one end side thereof,and a moving portion 55 b formed on the other end side thereof,extending in an axial direction of the rocker shaft 30 and bent to theoutside in the radial direction. The bent portion 55 a is inserted intothe cylinder head 10.

The continuous variable arm 53 is formed to have an almostlaterally-facing U shape in a side view. A laterally-facing U-shapedbase end 53 a is formed on a lower side in FIG. 5, and a contact portion53 b is formed on an upper side in FIG. 5. The base end 53 a has arecessed portion 53 c formed on an upper surface thereof. The recessedportion 53 c is formed to have an almost semi-spherical shapecorresponding to the spherical shape of the universal coupling 54 a andincorporated to be capable of oscillation by using the universalcoupling 54 a as a fulcrum.

On the continuous variable arm 53, a roller 53 d is arranged to becapable of oscillation at an intermediate position between the base end53 a and the contact portion 53 b. When the roller 53 d is brought intocontact with the cam 23 and the cam 23 is rotated, the continuousvariable arm 53 is caused to oscillate by using the center of theuniversal coupling 54 a as a fulcrum.

Reference number 56 in FIG. 5 denotes a transformation member. Thetransformation member 56 is formed to have a triangular tabular shapewhich is long on one end side, and a slide surface portion 56 a isformed on an upper-side surface in FIG. 5, and a transmission surfaceportion 56 b is arranged on a lower-side surface in FIG. 5. The slidesurface portion 56 a is formed to have a curvature equal to that of apad 57 (see FIG. 9) fixed to the cylinder head 10 and slidably movesalong an arc-like lower surface of the pad 57.

The transmission surface portion 56 b is formed such that a distancebetween the transmission surface portion 56 b and the slide surfaceportion 56 a has a predetermined value along the slide surface portion56 a . More specifically, the transmission surface portion 56 b isformed such that, when the transformation member 56 is slidably movedalong an arc-like lower surface of the pad 57, a member being in contactwith the transmission surface portion 56 b at a predetermined positionmakes a predetermined motion in a direction perpendicular to the pad 57with the movement of the transformation member 56.

A trench 56 c is formed in the transmission surface portion 56 b, andthe moving portion 55 b of the torsion coil spring 55 is engaged in thetrench 56 c. When the moving portion 55 b is engaged in the trench 56 c,the torsion coil spring 55 biases the transformation member 56 such thatthe transformation member 56 moves to the continuous variable arm 53side.

Furthermore, a semi-cylindrical joint 57 is arranged between thetransformation member 56 and the contact portion 53 b of the continuousvariable arm 53. The joint 57 is attached to the contact portion 53 b ofthe continuous variable arm 53 and slidably fitted on the transformationmember 56. The joint 57 is designed to absorb a change in a contactangle between the transformation member 56 and the contact portion 53 band to transmit a pressing operation of the continuous variable arm 53to the transformation member 56.

An operation of the continuous variable rocker arm mechanism 50 will beexplained with reference to FIG. 9. When a valve opening timing or avalve closing timing of the exhaust valve is to be retarded, the rockershaft 30 is caused to oscillate by the drive mechanism 90 in such adirection that the universal coupling 54 a of the connection member 54approaches the exhaust valves 14 and 15 with reference to a neutralposition.

The base end 53 a is pulled to the left by the universal coupling 54 a,and the continuous variable arm 53 moves to the left as a whole. On theother hand, the transformation member 56 is biased by the torsion coilspring 55 on the continuous variable arm 53 side. For this reason, thetransformation member 56 is brought into tight contact with the pad 57,and the roller 53 d is brought into contact with the cam 23. At thistime, since the cam shafts 21 rotate counterclockwise, an angle betweena start point of a cam nose and a contact point between the roller 53 dand the cam 23 is set to be widest, and the continuous variable arm 53is driven by the cam 23 later than that in the neutral state. As aresult, the valve opening timing or the valve closing timing areretarded.

On the other hand, when a valve opening or valve closing timing of anexhaust valve is to be advanced, the universal coupling 54 a of theconnection member 54 is caused to oscillate in such a direction that theuniversal coupling 54 a goes away from the exhaust valves 14 and 15 sidewith reference to the neutral position.

The base end 53 a is pulled to the right by the universal coupling 54 a,and the continuous variable arm 53 moves to the right as a whole. On theother hand, the transformation member 56 is biased by the torsion coilspring 55 on the continuous variable arm 53 side. For this reason, thetransformation member 56 is brought into tight contact with the pad 57,and the roller 53 d is brought into contact with the cam 23.

At this time, since the cam shafts 21 rotate counterclockwise, an anglebetween a start point of a cam nose and a contact point between theroller 53 d and the cam 23 is set to be narrowest, and the continuousvariable arm 53 is driven by the cam 23 earlier than that in the neutralstate. As a result, the valve opening timing or the valve closing timingare advanced.

The retarding and advancing adjustments are continuously performed bycontinuously adjusting an angle position of the rocker shaft 30.

As described above, the variable valve apparatus 20 can change a valveopening timing and a valve closing timing by making the drive mechanism90 cause the rocker shaft 30 to oscillate. For this reason, the valveopening timing and the valve closing timing are changed to make itpossible to increase an intake air flow and to achieve a reduction infuel consumption.

With this configuration, in the internal combustion engine comprisingthe variable valve apparatus 20 having the switching rocker armmechanism 40 and the continuous variable rocker arm mechanism 50, thefollowing control can be performed.

First, the operations of the switching rocker arm mechanism 40 and thecontinuous variable rocker arm mechanism 50 performed when an amount ofinternal EGR is optimized will be explained while comparing a “normaloperation” and an “internal EGR operation”. FIG. 6 is a graph showing arelationship between the phase and lift of the cam shaft 21. Referencesymbol EX denotes opening valves (lifts) of the exhaust valves 14 and15, and reference symbol IH denotes opening valves (lifts) of the airintake valves 12 and 13.

<Normal Operation>

The cam shaft 21 causes an exhaust stroke which opens the exhaust valves14 and 15 to slightly overlap an intake stroke performed by opening theair intake valves 12 and 13. An operation of the switching rocker armmechanism 40 at this time is shown in FIG. 8, and an operation of thecontinuous variable rocker arm mechanism 50 at this time is shown inFIG. 9. In the normal operation, on both the air intake valves 12 and 13side and the exhaust valves 14 and 15 side, an operation mode of theswitching rocker arm mechanism 40 is set to be off, and an operationmode of the continuous variable rocker arm mechanism 50 is set to anormal (neutral) mode.

More specifically, when the operation mode of the switching rocker armmechanism 40 is set to be off, oil pressure is not applied by the oilpressure supply mechanism 80, and engine oil is not supplied into thehollow portion 71 a in the switching rocker arm mechanism 40. For thisreason, the piston 73 is biased downward by an elastic force of thespring 74, and the notch 73 a is located at the window portion 71 b. Onthe other hand, the roller 41 c moves along the cam 22 by the rotationof the cam 22 rotated by the cam shaft 21, and the switching rocker arm41 oscillates about the rocker shaft 30 at predetermined intervals in adirection indicated by an arrow E in FIG. 8. However, even when thestrike arm 41 b is inserted into the window portion 71 b, the strike arm41 b is inserted into only the notch 73 a but not brought into contactwith the piston 73. Therefore, motion of the switching rocker arm 41 isnot transmitted to the shared rocker arm 60. Consequently, the switchingrocker arm mechanism 40 does not operate, and the air intake valves 12and 13 and the exhaust valves 14 and 15 are not driven.

In the continuous variable rocker arm mechanism 50, the rocker shaft 30is set at a neutral position by means of the drive mechanism 90.Therefore, the roller 53 d moves along the cam 23 by rotation of the cam23 rotated by the cam shaft 21, and the continuous variable arm 53oscillates about the rocker shaft 30 at predetermined intervals in adirection indicated by an arrow F in FIG. 9. In this manner, motion ofthe continuous variable arm 53 is transmitted to the shared rocker arm60 through the transformation member 56 and the intermediate arm 51, andthe air intake valves 12 and 13 and the exhaust valves 14 and 15 aredriven along a profile of the cam 23.

As described above, in the normal operation, by the continuous variablerocker arm mechanism 50, the air intake valves 12 and 13 and the exhaustvalves 14 and 15 are driven according to phases and lifts which changealong a solid line S.

<Internal EGR Operation>

In an internal EGR operation, on the air intake valves 12 and 13 side,the operation mode of the switching rocker arm mechanism 40 is set to beoff, and the operation mode of the continuous variable rocker armmechanism 50 is set to an early closing (advance) mode. On the exhaustvalves 14 and 15 side, the operation mode of the switching rocker armmechanism 40 is set to be on, and the operation mode of the continuousvariable rocker arm mechanism 50 is set to a normal (neutral) mode.

The operations of the switching rocker arm mechanism 40 and thecontinuous variable rocker arm mechanism 50 are summarized as follows.

TABLE 1 Optimization of amount of internal EGR Switching rockerContinuous variable arm mechanism rocker arm mechanism Air intake valveOFF Early closing Exhaust valve ON Normal

When the operation mode of the switching rocker arm mechanism 40 on theexhaust valves 14 and 15 side is set to be on, oil pressure is appliedby the oil pressure supply mechanism 80. As shown in FIG. 10, in theswitching rocker arm mechanism 40, engine oil is supplied into thehollow portion 71 a. For this reason, the piston 73 rises against theelastic force of the spring 74, and the circumference of the piston 73is positioned at the window portion 71 b. On the other hand, the roller41 c moves along the cam 22 by rotation of the cam 22 rotated by the camshaft 21, and the switching rocker arm 41 oscillates about the rockershaft 30 at predetermined intervals in a direction indicated by an arrowE in FIG. 8. When the strike arm 41 b is inserted into the windowportion 71 b, the strike arm 41 b is brought into contact with thecircumference of the piston 73. Therefore, motion of the switchingrocker arm 41 is transmitted to the shared rocker arm 60, and theexhaust valves 14 and 15 are driven along a profile of the cam 22. Anose 22 a of the cam 22 corresponds to reference symbol P in FIG. 6.

In the continuous variable rocker arm mechanism 50 on the air intakevalves 12 and 13 side, the rocker shaft 30 is rotated counterclockwiseby a predetermined angle by means of the drive mechanism 90 and set atan advance angle position. A fulcrum of oscillation of the continuousvariable arm 53 is distanced from the air intake valves 12 and 13. Inthis state, by rotation of the cam 23 rotated by the cam shaft 21, theroller 53 d moves along the cam 23, and the continuous variable arm 53oscillates about the rocker shaft 30 at predetermined intervals in adirection indicated by an arrow F in FIG. 11. In this manner, motion ofthe continuous variable arm 53 is transmitted to the shared rocker arm60 through the transformation member 56 and the intermediate arm 51, andthe air intake valves 12 and 13 are driven while being advanced withrespect to the profile of the cam 23.

As described above, in an intake stroke of the internal EGR operation,the air intake valves 12 and 13 are driven by the continuous variablerocker arm mechanism 50, and the exhaust valves 14 and 15 are driven bythe switching rocker arm mechanism 40. Therefore, the air intake valves12 and 13 open according to phases and lifts indicated by referencesymbol S in FIG. 6, and the exhaust valves 14 and 15 open according tophases and lifts indicated by reference symbol P in FIG. 6. Morespecifically, the exhaust valves 14 and 15 open at timings indicated byreference symbol P in FIG. 6. That is, since the exhaust valves 14 and15 open in the intake stroke, an exhaust gas temporarily exhausted fromthe cylinder 11 is taken into the cylinder 11 to cause an internal EGRoperation.

Since the lifts of the exhaust valves 14 and 15 at this time areconstant, an amount of internal EGR is constant. On the other hand,since an operation state of the engine is not constant, a requiredamount of EGR changes. For this reason, this fine adjustment isperformed by the operations of the air intake valves 12 and 13. Morespecifically, in order to prevent a reduction in NO_(x) from beinghindered due to an excessively small amount of internal EGR, the end ofclosing of the air intake valves 12 and 13 is made early to make itpossible to reduce an amount of intake itself, and the amount ofinternal EGR consequently relatively increases. FIG. 7 shows arelationship between closing end phases and amounts of air of the airintake valves 12 and 13 and a relationship between the closing endphases and the amounts of internal EGR of the air intake valves 12 and13. When the air intake valves 12 and 13 are closed in a phase S1 or S2slightly earlier than a standard closing end phase S0, an amount of airdecreases, and the amount of internal EGR increases.

As described above, the switching rocker arm mechanism 40 and thecontinuous variable rocker arm mechanism 50 are operated in conjunctionwith each other to make it possible to obtain a more appropriate amountof EGR and to purify an exhaust gas.

Operations of the switching rocker arm mechanism 40 and the continuousvariable rocker arm mechanism 50 in an engine braking operation will beexplained while comparing a “normal operation” and an “engine brakingoperation”. FIG. 12 is a graph showing a relationship between the phaseand lift of the cam shaft 21. Reference symbol EX denotes opening valves(lifts) of the exhaust valves 14 and 15, and reference symbol IH denotesopening valves (lifts) of the air intake valves 12 and 13.

<Normal Operation>

The cam shaft 21 causes an exhaust stroke which opens the exhaust valves14 and 15 to slightly overlap an intake stroke performed by opening theair intake valves 12 and 13. An operation of the switching rocker armmechanism 40 at this time is shown in FIG. 8, and an operation of thecontinuous variable rocker arm mechanism 50 at this time is shown inFIG. 9. In the normal operation, on both the air intake valves 12 and 13side and the exhaust valves 14 and 15 side, an operation mode of theswitching rocker arm mechanism 40 is set to be off, and an operationmode of the continuous variable rocker arm mechanism 50 is set to anormal (neutral) mode.

The operation of the switching rocker arm mechanism 40 and the operationof the continuous variable rocker arm mechanism 50 in the normal statewill not be explained because the operations are the same as those inFIGS. 8 and 9.

<Engine Braking Operation>

In an engine braking operation, on the air intake valves 12 and 13 side,the operation mode of the switching rocker arm mechanism 40 is set to beoff, and the operation mode of the continuous variable rocker armmechanism 50 is set to a normal (neutral) mode. On the exhaust valves 14and 15 side, the operation mode of the switching rocker arm mechanism 40is set to be on, and the operation mode of the continuous variablerocker arm mechanism 50 is set to an early opening (advance) mode.

The operations of the switching rocker arm mechanism 40 and thecontinuous variable rocker arm mechanism 50 are summarized as follows.

TABLE 2 Engine braking operation Switching rocker Continuous variablearm mechanism rocker arm mechanism Air intake valve OFF Normal Exhaustvalve ON Early opening

When the operation mode of the switching rocker arm mechanism 40 on theexhaust valves 14 and 15 side is set to be on, oil pressure is appliedby the oil pressure supply mechanism 80. As shown in FIG. 14, in theswitching rocker arm mechanism 40, engine oil is supplied into thehollow portion 71 a. For this reason, the piston 73 rises against theelastic force of the spring 74, and the circumference of the piston 73is positioned at the window portion 71 b. On the other hand, the roller41 c moves along the cam 22 by rotation of the cam 22 rotated by the camshaft 21, and the switching rocker arm 41 oscillates about the rockershaft 30 at predetermined intervals in a direction indicated by an arrowE in FIG. 14. When the strike arm 41 b is inserted into the windowportion 71 b, the strike arm 41 b is brought into contact with thecircumference of the piston 73. Therefore, motion of the switchingrocker arm 41 is transmitted to the shared rocker arm 60, and theexhaust valves 14 and 15 are driven along a profile of the cam 22. Thenose 22 a of the cam 22 corresponds to reference symbol L in FIG. 6.

As shown in FIG. 15, in the continuous variable rocker arm mechanism 50on the exhaust valves 14 and 15 side, the rocker shaft 30 is rotatedcounterclockwise by a predetermined angle by means of the drivemechanism 90 and set at an advance angle position. A fulcrum ofoscillation of the continuous variable arm 53 is distanced from the airintake valves 12 and 13. In this state, by rotation of the cam 23rotated by the cam shaft 21, the roller 53 d moves along the cam 23, andthe continuous variable arm 53 oscillates about the rocker shaft 30 atpredetermined intervals in a direction indicated by an arrow F in FIG.15. In this manner, motion of the continuous variable arm 51 istransmitted to the shared rocker arm 60 through the transformationmember 56 and the intermediate arm 51, and the air intake valves 12 and13 are driven while being advanced with respect to the profile of thecam 23.

As described above, in the engine braking operation, the air intakevalves 12 and 13 are driven by the continuous variable rocker armmechanism 50, and the exhaust valves 14 and 15 are driven by both theswitching rocker arm mechanism 40 and the continuous variable rocker armmechanism 50. Therefore, the air intake valves 12 and 13 open accordingto phases and lifts indicated by reference symbol N in FIG. 12, and theexhaust valves 14 and 15 open according to phases and lifts indicated byreference symbols M and L in FIG. 12. More specifically, the switchingrocker arm mechanism 40 opens the exhaust valves 14 and 15 at timingsindicated by reference symbol L in FIG. 12. That is, the exhaust valves14 and 15 open at a compression top dead center (TDC) to operate acompression brake. Since the lifts of the exhaust valves 14 and 15 areconstant, the braking effect is constant.

On the other hand, since the operation state of the engine is notconstant, a necessary braking force changes. For this reason, this fineadjustment is performed by the operations of the exhaust valves 14 and15 driven by the continuous variable rocker arm mechanism 50. Morespecifically, when the exhaust valves 14 and 15 start to open in a phaseM1 or M2 slightly earlier than a standard phase M0 to make an openingtiming early, an exhaust energy (amount of air) can be increased, andthe braking force is consequently relatively increased. FIG. 13 shows arelationship between opening start phases of the exhaust valves 14 and15 and the exhaust energy (amount of air) and a relationship between theopening start phases of the exhaust valves 14 and 15 and the enginebraking force.

As described above, when the switching rocker arm mechanism 40 and thecontinuous variable rocker arm mechanism 50 are operated in conjunctionwith each other, a more appropriate engine braking force can beobtained, and preferable drive feeling can be obtained.

As described above, according to the variable valve apparatus 20 for aninternal combustion engine according to the embodiment, a plurality offunctions such as execution of internal EGR, application of enginebraking, improvement in fuel consumption, and purification of an exhaustgas can be simultaneously exerted.

According to the present invention, valves are opened or closed by usingboth the switching rocker arm mechanism and the continuous variablerocker arm mechanism to make it possible to realize a plurality offunctions such as instantaneous switching of opening/closing timings ofthe valves and fine control of lifts.

Furthermore, transmission of oscillation displacement is selectivelyperformed as needed to make it possible to open or close a valve withoutdelay. The transmission of oscillation displacement is continuouslyperformed to make it possible to finely control the drive phase and liftof the valve. When fine adjustment of an amount of EGR is performedwhile performing the internal EGR, an exhaust gas can be purified.Engine braking can be applied, and the effect can be enhanced.

1. A variable valve apparatus for an internal combustion engine,comprising: a cam shaft arranged to be rotatable on a cylinder head ofthe internal combustion engine; a rocker shaft arranged to be capable ofoscillation in the internal combustion engine; a continuous variablerocker arm mechanism which is driven by a cam formed on the cam shaft,opens or closes at least one of an air intake valve and an exhaustvalve, and continuously makes a lift of the valve variable; and aswitching rocker arm mechanism which is driven by the cam formed on thecam shaft, opens or closes at least one of the air intake valve and theexhaust valve, and switches the lift of the valve in a stepwise manner.2. The variable valve apparatus for an internal combustion engineaccording to claim 1, wherein the switching rocker arm mechanismcomprises: a shared rocker arm which is supported on the rocker shaft tobe capable of oscillation and configured to drive the valve; a switchingrocker arm which is driven by the cam and arranged to be capable ofoscillation on the rocker shaft; and a transmission mechanism whichselectively transmits displacement from the switching rocker arm to theshared rocker arm.
 3. The variable valve apparatus for an internalcombustion engine according to claim 1, wherein the continuous variablerocker arm mechanism comprises: a shared arm supported on the rockershaft to be capable of oscillation and configured to drive the valve; acontinuous variable arm driven by the cam and arranged to be capable ofoscillation about a fulcrum arranged on the rocker shaft side; anintermediate arm supported by the rocker shaft to be capable ofoscillation and arranged between the shared arm and the continuousvariable arm; a transformation member which is arranged between theintermediate arm and the continuous variable arm and transmitsoscillation displacement of the continuous variable arm to the sharedarm through the intermediate arm; and a drive mechanism which causes therocker shaft to oscillate to displace the fulcrum.
 4. The variable valveapparatus for an internal combustion engine according to claim 1,wherein the internal combustion engine comprises the continuous variablerocker arm mechanism on an intake side and the switching rocker armmechanism on an exhaust side, and when the internal combustion engine isin an intake stroke, the exhaust valve is opened by the switching rockerarm mechanism, and the air intake valve is closed early by thecontinuous variable rocker arm mechanism.
 5. The variable valveapparatus for an internal combustion engine according to claim 1,wherein the internal combustion engine comprises at least one of theexhaust valves driven by the switching rocker arm mechanism and at leastone of the exhaust valves driven by the continuous variable rocker armmechanism per cylinder, and when the internal combustion engine is neara compression top dead center, the exhaust valve is opened by theswitching rocker arm mechanism, and the exhaust valve is opened early bythe continuous variable rocker arm mechanism.